The present invention relates to a connection arrangement which comprises a dental implant known per se, which can be inserted into the jaw bone, and an abutment to be fixed on the implant. At the top, on the head of the implant, an axial, downwardly extending receiving hole, which is preferably widened conically upward, opens out within an encircling implant shoulder. The lower root part of the abutment, which, when there is a conical inner configuration of the receiving hole, has a complementary conical outer contour, can be inserted into the receiving hole. For the reproducible positioning of the abutment, a non-rotationally-symmetrical receiving contour may be advantageously provided in the receiving hole and have relating to it a corresponding, non-rotationally-symmetrical outer mating contour on the root part of the abutment. The non-rotationally-symmetrical contours complementing one another likewise represent a rotational securement for the inserted abutment, the rotational securement in fact already being brought about by the cone-cone connection between the inner cone of the implant and the conical root part on the abutment.
From the bottom of the receiving hole there extends further downward a coaxial. internally threaded hole for the engagement of a base screw disposed axially in the abutment, so that the abutment is fixed on the implant by screwing in of the base screw. The base screw is introduced into the abutment, the head of the base screw being supported in the abutment, while the threaded shank of the base screw protrudes out of the abutment at the bottom and engages in the internally threaded hole in the implant. Connection arrangements of this type are used both for straight abutments and for angled abutments. The base screw secures the abutment axially on the implant andxe2x80x94if the implant and abutment have non-rotationally-symmetrical contours engaging in one anotherxe2x80x94also against rotation in addition to the cone-cone connection. The selectable rotational positions in which the abutment can be fixed are limited by the shaping of the non-rotationally-symmetrical contours, for example the number of corners of polygons used.
The basic structure of the implantxe2x80x94but still without a non-rotationally-symmetrical receiving contour, preferably an internal polygonxe2x80x94is known for example from the monograph by SCHROEDER/SUTTER/BUSER/KREKELER: Oral Implantology, Georg Thieme Verlag Stuttgart, 2nd edition 1996, page 127. Such an implant has the implant head at the top and the shank part at the bottom, the implant head terminating at the very top with the radially encircling implant shoulder and it being possible, depending on the type of implant, for there to be an external thread on the shank part. The implant shoulder surrounds the mouth of the receiving hole conically narrowing axially downward, whereby the inner cone is produced. At the bottom of the hole, the receiving hole merges into a coaxial internally threaded hole of reduced diameter, which extends apically into the shank part and has the internal thread.
WO 94/09717 and WO 97/14371 disclose implants of the type described above which have within the receiving hole an internal polygon arranged at a distance from the implant shoulder. Complementing this, there are external polygons on the respective abutments. The internal polygon in the implant brings with it considerable advantages as a positioning aid for the reproducible positioning of the inserted abutment in conjunction with the superstructures which are adapted by the prosthetist or dental technician, and possibly as rotational securement. The angle of rotation with respect to the longitudinal axis of an inserted abutment whose neck part protruding above the implant shoulder is not rotationally symmetrical must be transferred to a dental model in relation to the anatomy surrounding the implantation site. In the case of the implant according to U.S. Pat. No. 4,960,381, the internal polygon is additionally used beforehand for screwing into the bone, in that a socket wrench is inserted into the internal polygon.
WO 97/14371 discloses a connection arrangement between an implant with an internal polygon in the conical receiving hole and an abutment with a corresponding, apically extending root part. In the case of this design, there is in the root part of the abutment, close to the lower outlet of the passage, a radial groove for receiving a spreading ring. The spreading ring is pushed onto the shank piece of the base screw and comes to lie under the screw head. The base screw can then be pushed with the screw head first into the root part, until the spreading ring slides into the radial groove. The abutment preassembled to this extent with the base screw and the spreading ring is inserted into the receiving hole of the implant. In the case of a straight abutment, the passage is axial. In the case of an angled abutment, the passage is likewise angled and may have an additional vertically oriented lateral opening for the perpendicular insertion of the screwing implement. The screwing implement is inserted through the passage or the lateral opening and the threaded shank of the base screw is thus screwed into the internally threaded hole of the implant. The screw head of the base screw presses on the spreading ring, which introduces the tensile force into the abutment, so that the latter is drawn into the receiving hole.
The connection arrangement according to WO 97/14371 has the major advantage that the screw head of the base screw does not have to be introduced from above into the passage of the abutment. This allows the passage at the coronal end, in which an internal thread for an occlusal screw may be provided, to be shaped such that it is dimensioned smaller than the diameter of the screw head of the base screw. The space available on the superstructure, for example on the artificial tooth crown, limits the size of the insertable occlusal screw. In the interests of the strength of the screw connection, however, a base screw which is not reduced in diameter in relation to the occlusal screw but has the same diameter may be used. The main resultant advantage is that screws of the same diameter as the base screw and as the occlusal screw that can be screwed into the coronal end can be used; i.e. the internally threaded hole in the implant and the internally threaded hole in the coronal part of the abutment have the same diameter. This serves for the reliability of the screw connections and simplifies the system which forms the implants of various configuration with the variety of structural parts and the set of implements.
With the connection arrangement according to WO 97/14371, significant progress was achieved in comparison with the previously applicable state of the art. The forming of the internal radial groove in the abutment and the use of the spreading ring disposed on the base screw and received in the radial groove cannot, however, be regarded as the ultimate, complete solution. The mechanical working of the radial groove in the abutment and a radial groove on the shank of the base screw in which the spreading ring is seated during the pushing of the base screw into the abutment must take place with high precision and altogether requires a not inconsiderable outlay in terms of working and inspection. Bearing in mind the relatively small dimensions of the connection arrangement, the relatively high forces to be absorbed under alternating loading and the enormous requirements for reliability, there is the need to retain the basic advantages of the connection arrangement but to lower the production outlay and, in particular, further increase the reliability. The head of the base screw presses on the relatively narrow annular surface at the top of the spreading ring and the spreading ring is for its part seated in a pressing manner on a likewise narrow horizontal annular surface within the radial groove.
In view of the need to improve the functional reliability of the previously known connection arrangement and at the same time lower the production outlay, the invention is based on the object of proposing a perfected connection arrangement. A connection arrangement between an implant and a straight or angled abutment that is distinguished by extremely high reliability is to be provided. The abutment must at the same time allow itself to be fixed in a practical way on the implant and must not be loosened even as a result of micro-movements. Moreover, the connection arrangement is to comprise a small number of uncomplicated parts and consequently be inexpensive to produce. The parts of the connection arrangement should have a system character and consequently be able to be used for different variants of the connection arrangementxe2x80x94i.e. for combination with various abutments. The main advantages of a connection arrangement where the base screw is inserted with the screw head first into the root part of the abutment are to be retained. An additional objective here is that the flexurally greatly stressed base screw should have a small longitudinal force and a loosening moment that is as high as possible.
Provided in the abutment is an inlet, which could be an axial passage. From the side of the root part, a base screw can be pushed with its screw head first into this inlet, as far as a head zone. The threaded shank of the base screw, which is reduced in diameter with respect to the screw head and, in the inserted state, protrudes from the root part of the abutment, is intended for engagement in the axially extending internally threaded hole in the implant. After insertion of the base screw into the abutment, a support ring is pushed over the threaded shank of the base screw into the mouth of the inlet and is fixed in its intended position. Fixing takes place by radial welding to the lower edge of the abutment. An alternative possibility is for the support ring to be adhesively bonded to the inner wall of the abutment, for which purpose a biocompatible and officially approved cement or adhesive is used. A further alternative for the fixing of an inserted support ring is to provide that the lower edge of the abutment is extended in order to bend said lower edge around inward after the pushing in of the support ring, i.e. gripping under the lower edge of the support ring. The base screw then rests in each case on the fixed support ring.
It has proven to be favorable to provide the support ring on its upper and lower edges with an internal beveled surface and to shape the part of the screw neck situated beneath the screw head such that it widens conically toward the screw head. Consequently, in the screwed state, a sloping surface of the screw neck presses against the internal beveled surface of the support ring. With the support ring having an identical contour at the upper and lower edges, it does not matter which edge of the support ring is at the top. To give it elasticity, the support ring could have a penetrating vertical slit or partial slits. In a special configuration, the support ring has an internal thread complementing the threaded shank of the base screw, so that the support ring must be screwed on when it is fitted onto the base screw.
The connection arrangement comprising the abutment with the inserted base screw, which is held by the introduced support ring, and the implant is put together in the following way. The abutment is brought with the threaded shank of the base screw first up to the receiving hole of the implant, so that the threaded shank is above the internally threaded hole of the implant. If there is a non-rotationally-symmetrical receiving contourxe2x80x94for example an internal polygonxe2x80x94in the implant and a complementary outer mating contour on the abutment, it must be ensured that the two contours are in a congruent position when they are brought into place. A suitable screwing implement is used to reach through the penetrating axial passage in the abutment or a provided lateral opening into the engagement contour of the base screw and screw the latter into the internally threaded hole. Consequently, the abutment is drawn increasingly deeper and more firmly into the receiving hole, the screw neck pressing onto the support ring fixed in the abutment.
Then the further superstructure can be fitted onto the abutment, the method by which it is fastened depending on the design of the abutment respectively used. If the abutment has an internally threaded hole, a method which comes into consideration is a screw connection with an occlusal screw, which is advantageously of the same diameter as the base screw. In the anterior tooth area, or if the implant is in a slanted position, where occlusal screw connection is not possible, an abutment with a lateral hole will be used for the transversal screw connection of the fitted-on crown cap. In the case of solid abutments, the superstructure is cemented onto the abutment.
The invention is responsible for providing a connection arrangement between an implant and an abutment which is distinguished by very high functional reliabilityxe2x80x94i.e. being held together in a stable and precise manner in the fitted statexe2x80x94and advantageous fitting and removal properties. The connection arrangement according to the invention can be produced at efficient production costs and is suitable in particular for implants with a non-rotationally-symmetrical receiving contour in combination with straight or angled abutments with a corresponding non-rotationally-symmetrical outer mating contour.